Field of the Invention
The present invention relates to a solid-state imaging apparatus and a method of controlling the same.
Description of the Related Art
Along with an increase in number of pixels of an image sensor such as a CMOS sensor in a recent digital camera, there is an increasing need for high-frame rate shooting of outputting 1920×1080 pixels at 30 fps or 60 fps like a full HD movie.
To meet this need, a pixel mixing method of mixing pixel output signals is known as a method of decreasing the number of pixels for implementing high-frame rate shooting by a CMOS image sensor with a large number of pixels by switching a driving method. In the pixel mixing method, the frame rate is increased by decreasing the data rate by mixing and outputting a plurality of pixels in a specific cycle in the CMOS image sensor.
A pixel mixing method disclosed in Japanese Patent No. 4723994 mixes and outputs pixel signals on a plurality of rows by causing a row selection circuit to simultaneously select and output a plurality of pixel rows. According to Japanese Patent No. 4723994, it is possible to mix and output pixel signals without increasing the power consumption, as compared with a method of averaging signals in the vertical direction using conventional capacitors.
However, when the method described in Japanese Patent No. 4723994 is used, as the output difference between a plurality of pixels whose pixel signals are to be mixed and output is larger, the linearity of the output with respect to the input may not be maintained.
The problem that the linearity is not maintained arises especially for an object having high contrast and high-frequency stripes at the time of actual imaging. If, for example, an object on which a black and white pattern is repeated at a high frequency is imaged by a CMOS image sensor in which color filters of two or more different colors are periodically arranged in respective pixels, the linearity is sequentially lost from a pixel of a color which processes a larger signal amount. If the input/output linearity is lost, a false color is output, thereby degrading the image quality. If the input/output linearity cannot be maintained, a method of uniformly increasing the current values of all pixels which output signals is plausible. However, this method increases the power consumption.